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[Frama-c-discuss] z3 failure

  • Subject: [Frama-c-discuss] z3 failure
  • From: siegel at (Stephen Siegel)
  • Date: Sun, 6 Oct 2013 17:06:46 -0400

I have a very simple example (below) which I want to verify with frama-c + Jessie.  The VCs are discharged easily by Alt-Ergo, CVC3, and CVC4.  However they are not discharged by Z3.  This is surprising since Z3 is a very powerful prover.   I'm wondering if anyone has any idea what is going on, or how to look into it.

I am using Z3 4.3.1.  There are two VCs.  One, "copy_safety" is discharged by Z3 very quickly.  The other, "copy_ensures_default" runs forever. I've moved the timeout to 60 seconds, and it still times out.

BTW, this warning appears with both VCs:

WARNING: '=' cannot be used in patterns

Here is the program copy.c:

  @ requires n>=0 && \valid(a+(0..n-1)) && \valid(b+(0..n-1)) ;
  @ ensures \forall integer i ; 0 <= i < n ==> a[i] == b[i] ;
  @ assigns b[0..n-1] ; 
void copy(int n, double a[], double b[]) {
  int i = 0;

    @ loop invariant 0<=i<=n;
    @ loop invariant \forall integer j ; 0<=j<i ==> b[j] == a[j] ;
    @ loop variant n - i ;
  while (i < n) {
    b[i] = a[i];